The present invention relates to the protection of various construction materials from the effects of heat and fire.
There are in general three major categories of materials which provide heat-insulating or fire-retarding characteristics when applied to the surface of construction materials. The most common of these are porous or fibrous materials which exhibit low heat conductivity due primarily to the presence of air trapped in the pores or among the fibers of a fibrous batting. In general, the heat conductivity of these materials is not altered by fire or by high temperature, and the heat transfer through the material as a function of time can be generally represented by a straight line up to the point of melting. However, most of these materials melt by the temperature of 1500.degree. to 1800.degree. C. and thus are limited in their usage. For example, they cannot be used as insulating material for rockets where temperatures well in excess of the melting point may be reached.
A second group of materials comprise the ablative materials. These are materials that go through thermal, chemical and/or mechanical degradation in a manner that absorbs or dissipates energy. Aluminate sulfate hydrate is an example of such material. These materials do find use in the rocket industry because of their ability to withstand high temperatures, as well as their significant resistance to heat transfer. Thus, for example, if one side of a 10 mm. thick, porous, ceramic plate is exposed to a temperature in the range of about 750.degree. to 800 .degree. C., the other side will reach 200.degree. C. in about five to ten minutes. When, however, a 10 mm. thick, porous, ablative type material is subjected to the same treatment, it will take more than an hour for the opposite side to reach 200.degree. C.
A third group of materials is the intumescent materials. Ordinary intumescent materials are compositions that foam or otherwise expand in fire or high temperature conditions to produce insulating material. Within this group are the intumescent coating materials, that is, materials which are specifically designed to be applied in the form of a paint or the like where effect can be illustrated by the treatment of a metal plate. If one side of a 1.6 to 2 mm. metal plate is exposed to a temperature of 950.degree..+-.50.degree. C., the opposite side will reach 200.degree. C. in about twenty to thirty seconds. On the other hand, if the same metal plate is provided with a coating of an intumescent paint, and the painted side is exposed to the same high temperature, the opposite side will not reach 200.degree. C. until one or two minutes have expired.